Vertical shaft impact crushers are generally known in which centrifugal force is used to hurl large rocks against an impact surface, thereby to obtain smaller crushed rocks. Rock material is typically fed into a rotating impeller which hurls the rock material against a plurality of anvils disposed about the impeller. In the alternative, the rotating impeller throws the rock material against a bed of already crushed rock instead of the anvils. In either event, the rock crusher processes relatively larger rock material into relatively smaller crushed rock.
One important consideration in the design of rock crushers is the extension of the useful life span of the equipment. It will be appreciated that certain of the components come into direct contact with the rock material and therefore are subject to wear. The wear components are typically releasably attached to the rock crushing apparatus so that they may be removed and replaced. Other components are intended to be permanent, and therefore must be protected from direct contact with the rock material. The non-wear components are usually more permanently attached to the crusher apparatus.
For example, in a vertical shaft impact crusher of the "open table" type, the rotating impeller comprises a generally flat table having multiple shoe assemblies projecting from a top surface of the table near its periphery. The shoe assemblies typically comprise a support bracket attached to the table and a shoe releasably secured to the bracket. Rock material is dropped near the center of the table and, under centrifugal force, moves toward the periphery of the table where the shoes direct the large rock material toward an impact surface surrounding the table assembly, typically an anvil ring. The table is mounted on a flywheel attached to a rotating shaft. In this example, the shoes and anvil ring contact the rock material and therefore are wear components which should be attached to the crusher apparatus in such a manner that they are easily removed and replaced. The table, flywheel, and shaft are shielded from direct impact and therefore are more permanent, non-wear components.
Conventional rock crushers often use fasteners, such as bolts, to attach the shoe to support bracket. In such an arrangement, bolt holes extend through the bracket and corresponding threaded holes are formed in the shoe. The bolt holes and threaded holes have substantially the same size and are aligned so that bolts inserted therethrough releasably secure the shoe to the bracket. It will be appreciated that as the shoe assemblies are rotated by the table, a significant shear force develops between the fixed bracket and removable shoe. The shear force is quite large, particularly for heavier shoes, and therefore a significant risk exists that the bolts will be sheared and the shoes thrown.
In addition, conventional vertical shaft impact crushers often have a liner to protect the bracket from rock material bouncing off of the anvil ring. The liner is typically bolted in place and covers an outside face of the bracket. As the table spins, the centrifugal force acting on the shoe and bracket cause deflections in the bracket which increase in magnitude proportional to the height of the bracket above the upper surface of the table. The uneven deflections across the height of the bracket act to pry the bottom of the liner away from the bracket, thereby breaking the bolts from the bracket.
The present invention is provided to reduce the shear forces between the bracket and the shoe and/or to reduce prying forces between the bracket and the liner.